As thorough as Mr. Kurz is, this is most likely covered somewhere, so forgive me if it is. When I put my feet in front of me seated on the floor and reach down and touch my toes I have noticed that my legs start going numb. Is this normal or should call 911 now?

After a few weeks of stretching, I have also noticed that if I don't sit properly, my back goes numb. In January, it was an effort to sit up with a straight back and both feet flat on the floor.

It sounds likeyou may have over stretched the lower back.This could have occured through rounding your back as you've reached forwards.
It could also explain why your lower is having a hard time supporting your torso when you sit up.

My advice would be to drop the stretches that involve leaning or reaching forwards and see if matters improve.